1. Field of the Invention
The present invention is directed to an expandable sequence control system, and more particularly to a sequence control system having a central controller unit and a plurality of separate I/O interface modules to which a plurality of I/O devices are connected for being sequentially controlled by the central controller unit and which are interconnected by means of flexible cables.
2. Description of the Prior Art
Sequence control systems have recently been required to control an increased number of I/O devices, such as machines or sensors, with a single central controller unit so as to meet a sophisticated combination of the devices being controlled in a modern assembly line or other industrial operations. For this purpose, it is a common practice to add to the system a plurality of I/O interface modules having terminals for connection with the I/O devices. Exemplary of the prior system having a plurality of the I/O interfaces is schematically shown in FIG. 1, in which a central controller unit 1 and I/O interface modules 2 are mounted together on a mother board 3 with edge connectors 4 projecting on the bottom thereof inserted in corresponding sockets 5 formed on the mother board 3 so that the central controller unit 1 and the I/O interface modules 2 are interconnected by way of a bus line incorporated in the mother board. Each of the I/O interface modules 2 is provided on its top face with a terminal block 6 for connection with plural I/O devices to be controlled by the central controller 1. The combination of the edge connectors and the sockets can facilitate the interconnection of the I/O interface modules for the purpose of expanding the system, however, it should result in a fixed disposition of the I/O interface modules on the mother board, affording no flexibility in spatial arrangement of the I/O interface modules. In fact, such flexibility may be required and most preferable for easy and proper wiring operation between the I/O interface modules and the corresponding I/O devices located on different sites as well as for space-saving purposes when a large number of the I/O devices are to be connected to the central controller unit using a corresponding number of the I/O interface modules.